Sunrise 5:08 AM   Sunset 10:42 PM Moonrise 9:54 AM   Moonset 2:41 AM

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FXAK68 PAFC 141258 AFDAFC

Southcentral and Southwest Alaska Forecast Discussion National Weather Service Anchorage AK 458 AM AKDT Tue May 14 2024

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3/Today through Thursday night)...

The cold upper level low responsible for showers (and a few thunderstorms with hail) over Southcentral yesterday is exiting south into the Gulf this morning. Vorticity-maxima rotating around the north side of the low continue to produce isolated showers early this morning, primarily from the Talkeetna Mountains south to the Mat Valley and through Tahneta Pass into the western Copper River Basin. Meanwhile, a surface low over the northeastern Gulf is being pulled back westward toward the upper low center.
Middleton Island radar imagery shows a North-South oriented band of rain tracking westward across the northern Gulf and southeastern Prince William Sound, including Cordova. Further west, mostly clear skies can be found from Kodiak Island north to the Kenai Peninsula and much of the Susitna Valley.
Temperatures have once again dropped into the 30s, with isolated areas down below freezing.

The upper level low will exit eastward across the Gulf today, though cyclonic flow aloft, with embedded vorticity.maxima will continue to transit Southcentral. Slightly warmer temperatures in the upper atmosphere means conditions won't be quite as unstable today as they were yesterday. Still expect increasing showers this afternoon, but fewer showers than Monday and no thunderstorms. The favored areas for scattered showers will be the Mat-Su near the Talkeetna Mountains (roughly Willow to Palmer) along with the Copper River Basin - especially along the Tok Cutoff and north side of the Wrangell Mountains.

An upstream ridge of high pressure will build eastward tonight, then move overhead of Southcentral on Wednesday. This will cap off convection and lead to widespread sunny skies and warm temperatures. With a surface high building up from the Gulf, expect stronger sea breezes along the coast. This will lead to somewhat cooler temperatures for coastal communities compared to inland areas.

A dissipating front from a deep low in the Bering Sea will approach Kodiak Island and the western Gulf on Thursday. There will be very little forcing left, but likely enough to produce areas of very light rain. This will also lead to increasing clouds across the western tier of Southcentral Thursday through Thursday night. Model spread is quiet large with regard to the eastward progression of the long-wave trough and handling of individual short-waves. Thus, it is not clear whether any precipitation will make it up to Southcentral.

-SEB

.SHORT TERM FORECAST SOUTHWEST ALASKA, THE BERING SEA AND THE ALEUTIANS (Days 1 through 3/ Today through Thursday morning)...

The building ridge over the eastern Bering continues to move into Southwest Alaska this morning, providing calmer conditions for much of the area through tonight. This brief period of calmer weather will be short lived however, as a Kamchatka low in the western Bering continues to move eastward towards the western Alaska coastline.

The Kamchatka low's front extends across the entire western Bering, producing widespread gale force winds through tomorrow morning. Warm air behind the front will cause the majority of precipitation to come in the form of rain as the low progresses eastward. By Wednesday morning, the range of gale force winds will be limited mainly to Nunivak Island and the Kuskokwim Delta before the system weakens further in the afternoon hours.
Widespread precipitation will occur along the western coastline of Alaska through at least Thursday afternoon. With the ridge settled over mainland Alaska by this time, there is still some model disagreement to the eastward shift of the ridge and how it will effect the placement of the frontal precipitation across Southwest.

A new shortwave low is also expected to impact the western Aleutians Wednesday night into Thursday afternoon. While the exact timing and intensity of the system is uncertain, it does appear that some precipitation will be likely as it moves eastward before dissipating Thursday night.

-BS

.LONG TERM FORECAST (Days 4 through 7: Thursday night through Monday)...

The long term forecast for the Southern Alaska will begin with a ridge over the Gulf of Alaska sliding east as a shortwave trough rounds the base of a longwave upper-level trough situated over the Bering and moves over Southwest Alaska. Models quickly diverge with regard to the evolution of this system, adding plenty of uncertainty right at the beginning of the long term forecast. All guidance has the development of a surface low near the AKPen by Friday as the shortwave deepens. However, both the GEM and EC try to hold onto the downstream ridging longer, driving the low and its moisture into Southcentral. The GFS pushes the ridge south and provides a more progressive solution with the low tracking east with only scattered showers along the western slopes of the interior and coastal mountains. This system then exits to the east late Saturday.

Sunday may offer a reprieve from any extensive cloud cover and/or shower activity across the Southern Mainland. But, again, all models are struggling with the track of various shortwaves embedded within the longwave trough. While guidance shows a ridge trying to build north from the North Pacific and western Gulf, the EC and GEM quickly move the ridge axis east over the eastern Gulf. This solution would place the entirety of the Southern Mainland on the back side of the ridge with the resultant southwesterly flow lending to a more unsettled pattern with various waves moving along the Aleutian Chain and across the AKPen and Kodiak Island. The result would be more cloud cover and chances for rain across the region. The GFS is the more amplified solution, with a more northerly building ridge remaining in place longer. This result would slow any upstream storm systems and likely result in a more northerly storm track, keeping conditions much more tranquil across the Southern Mainland. Given the consistency of the GFS and a trend of the EC and GEM ensembles leaning more toward the GFS, the long term is weighted more toward the stronger ridge solution.

For the Aleutians and Bering, the longwave trough situated over the region will likely keep conditions cool and unsettled through the long term. Any ridging between storm systems would be brief, with the best chance for high pressure over the Bering late Friday into Saturday. Any warmer air associated with the ridge, though, would likely result in widespread stratus and fog due to the warmer air riding over the cold open waters.

-TM

AVIATION

PANC...VFR conditions and light winds will persist.

King Salmon Airport, Naknek River, Alaska, Tide feet

Omakstalia Point
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Tue -- 04:42 AM AKDT     Moonset
Tue -- 05:58 AM AKDT     Sunrise
Tue -- 06:18 AM AKDT     -0.04 feet Low Tide
Tue -- 09:48 AM AKDT     7.92 feet High Tide
Tue -- 11:53 AM AKDT     Moonrise
Tue -- 07:34 PM AKDT     0.56 feet Low Tide
Tue -- 09:38 PM AKDT     5.22 feet High Tide
Tue -- 10:49 PM AKDT     Sunset
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Omakstalia Point, Naknek River, Alaska, Tide feet

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